Printed educational material often contains questions, the answers to which must be provided by the reader and checked against a set of answers. Thus, in exercise books relating to natural sciences or other subjects, problems are set forth in a part of the book, and the solutions to the problems are set forth in a different part of the book, e.g. an appendix, to which the reader must continuously refer. In more complex cases, a text may be provided in which some words or figures are missing and the missing words or figures are supplied in a different part of the book. The necessity of constantly referring to a different part of the exercise book creates inconvenience and fatigue, is the source of not uncommon mistakes, such as when the reference numerals or other indications which correlate the questions to the corresponding answers are not accurate, and greatly limits the possibility of inserting within the printed text indications that must be supplied by the reader and may present increasing degrees of difficulty, in order gradually to advance the learner's knowledge. It would be highly desirable to provide printed matter which includes elements which cannot be read unless the reader wishes it, e.g. answers to questions or data which must be supplied by the reader.
In general, graphic matter, in particular printed texts, often contains information, which it is desired to keep private and protect from casual prying. For instance, information as to the balance of bank accounts is often exposed to the eyes of strangers and is readable at a glance; or certain confidential data may be contained in office documents which pass through the hands of employees who may not be completely trusted not to divulge them. Such texts therefore cannot be transmitted by such widely used means as telecopier apparatus. It would be desirable to permit creation and transmission of such matter in such a way as to assure that it cannot be read and understood by unauthorized persons who may see it or gain access to it.
Identifying graphic matter, such as words or numbers, is often included in documents to identify their origin, their destination etc. Such identifying graphic matter, however, can easily be reproduced or counterfeited and is often unreliable. It would be desirable to find a way to prevent such reproduction and counterfeiting.
Authentication of documents is desirable in a number of other instances. For example, diplomas or certificates of various kinds may be counterfeited and the agency, such as a public office or an institute, that is purported to have issued them, may find it difficult to check their authenticity as many years are supposed to have passed since they have been issued. Again, public offices may not have the time and/or the personnel for checking the authenticity of documents submitted to them in support of an application for a registration, a compensation, and so on. Further, tickets which are supposed to be issued to specified persons for admission to performances or games or the like, may be lost or stolen or counterfeited, and this is true of cards required to obtain admission to restricted premises, such as offices or laboratories engaged in confidential work; and the problem exists in checking whether the ticket or card has truly been issued to the person presenting it. As far as it is known to the applicant, no satisfactory solution to the aforesaid problems has been offered so far in the art. Also, in the case of fiscally relevant documents, such as bills, which purport to have been issued by a person or company to another person or company, with respect to the merchandise supplied or services rendered, it would be highly desirable to provide means for permitting the competent authority easily to determine whether any particular bill is truthful, viz. has been issued by the person or company purporting to have issued it, and is regular in all respects, whereby to prevent the counterfeiting of such bills or the preparation of bills that do not originate with recognized suppliers of bills or services or are irregular in other respects.
The prior art has dealt with these problems, or at least with part of them, essentially in three ways: by encoding, by scrambling and by encryption. Encoding is a complex procedure that cannot be used in everyday office or administrative work and which requires special training. Furthermore codes are easily broken unless they are so complex as to be usable only in very special circumstances. Scrambling is usually carried out in real time, viz. a message must be scrambled, transmitted and unscrambled concurrently. If it is not, there is time to unscramble the scrambled message by well known methods, based e.g. on the frequency of the letters of the alphabet in the languages. Furthermore, an apparatus which permits to read a scrambled message, also permits to scramble a clear message, whereas it would be highly desirable, and it is a purpose of this invention, as will appear hereinafter, to provide graphic matter that may be read by persons that are not authorized nor capable of producing it.
Encryption methods are known which are based on the transformation of an original image into a coded image by means of a key grid and visualization of the original image from the coded image by optical means are disclosed e.g. in U.S. Pat. Nos. 3,914,877. Such encryption methods however are more or less complex and lengthy and they cannot be carried out in the course of ordinary printing processes. They are therefore not applicable to the production of documents or to their transmission.
Cryptographic systems, based on public key cryptosystems, are described e.g. in the article by P. G. Comba "Exponentiation cryptosystems on the IBM PC", in IBM Systems Journal, vol. 29, No. 4 (1990), 526-538. While they may afford a high degree of secrecy, they are too complex to be currently used by unspecialized personnel in normal office procedure and for widespread use. Further, they--like other systems--are highly sensitive to noise.
It is a purpose of this invention to provide graphic matter, in particular printed texts, that cannot be read and understood except by authorized persons.
It is another purpose to provide such matter in an easy and economical way, as a part of conventional printing operations.
It is a further purpose to provide such matter which may be transmitted by means of conventional apparatus, in particular by telecopier.
It is a still further purpose to provide such matter which permits authentication of documents carrying it and of photostatic or other copies of an original document.
It is a still further purpose to provide an apparatus and a process for producing and visualizing and/or reading such graphic matter.
It is a still further purpose to provide such apparatus and process that permit the transmission of such graphic matter in a form that cannot be visualized and/or read by unauthorized persons and subsequently visualizing and/or reading the same.
It is a still further purpose to provide apparatus and process for authenticating, by means of such graphic matter, documents, such as fiscally relevant documents, e.g. bills, receipts and the like, or documents bearing the seal of a company or a public authority or the like, or tickets or admission cards.
Other purposes of the invention will become apparent as the description proceeds.